This invention solves a problem that arises in the playing of tennis when out-of-bounds balls are deflected back into the playing area after striking an enclosing wall or fence. Such balls are not only distracting to the players but can be dangerous if they are inadvertently stepped upon during play. The placing of soft nets around the field to absorb the energy of errant balls has been suggested but does not suffice since a positive entrapment is required really to provide an adequate safety factor. The present invention offers positive entrapment of errant balls by means of an inexpensive novel structure.